A Flutter

1. The act of fluttering; quick and irregular motion.
2. A state of agitation.
3. An abnormal rapid pulsation of the heart.
4. (uncountable, aerodynamics) An extremely dangerous divergent oscillation caused by a positive feedback loop between the elastic deformation of an object and the aerodynamic forces acting on it, potentially resulting in structural failure.
5. (Britain) A small bet or risky investment.
6. A hasty game of cards or similar.
7. (audio, electronics) The rapid variation of signal parameters, such as amplitude, phase, and frequency.